Hey Ken. Thanks for the information about a loose collar. Perhaps it is a function of the Gimbal. The iShoot collar for the 180-600 works well on my Gimbal, no issues with rotation or moving the lens forward and backward for balance. I just looked at Steve's video on balancing a gimbal after reading your post but I could not find the loose collar/gimbal video and would appreciate a link. Perhaps it is just to change from landscape to portrait orientation - a good idea. I will plan to loosen the collar on gimbal mounted lenses, something I have not done in the past.
I do not plan to use my made in China Nikon 180-600 on my Made in the USA gimbal, However, I do plan to use my made in China Nikon 800 6.3 PF lens with my made in the USA Hejnar replacement foot on a gimbal and will loosen the collar the next time I mount the lens on my made in the USA gimbal.